1. Field of the Invention
The present invention relates to methods of manufacturing semiconductor packages, more particularly, to improved lead frames used in semiconductor packages.
2. Description of the Related Art
To meet the requirement of modem electric products being delicate, designs of semiconductor package are aiming at minimizing volume and thickness. However, such products tend to be multiple functions; thus sizes of semiconductor die to be packaged are enlarged. To make the semiconductor package have minimized volume and large dies is what persons skilled in this field expect.
Referring to FIGS. 1, 2, or 3, a conventional method of manufacturing semiconductor packages comprises steps of (a) providing a lead frame 11 which comprises a die pad 111, a plurality of connecting parts 112 and a plurality of leads 113, wherein the die pad 111 is lower than the leads 113, and the connecting parts 112 connect the die pad 111 and the leads 113; besides, the lead frame 11 made of copper retains appropriate flexibility; furthermore, inner fingers used in connecting circuits inside the package and/or outer fingers used in connecting circuits outside the package are etched in proper positions of the lead frame; (b) mounting a die 12 onto the die pad 111 and electrically connecting the lead frame 11 and die 12 by bonding wires 13; (c) providing an upper mold 14 and a lower mold 15, wherein the upper mold 14 and lower mold 15 are located at an upper side and a lower side of the leads 113, respectively; the lead frame 11, die 12, and bonding wires 13 are enclosed in a mold cavity formed by the upper and lower molds 14 and 15 thereby, and the leads 113 are allowed to protrude outwards from the mold cavity. After fabricating such a construction, it can be proceeded with (d) applying an encapsulant through a filling hole co-formed by the upper mold 14 and the lower mold 15; and (e) forming an encapsulant 16 after encapsulating and removing the upper and lower molds 14 and 15 to complete the package.
For the purpose of preventing the die pad 111 of the lead frame 11 from exposure out of the encapsulant 16, an appropriate distance between the die pad 111 and the lower mold 15 should be kept. Therefore, the thickness of the semiconductor package cannot be reduced. In addition, when the dies to be packaged are too thick to fit the mold size, such dies should be grinded and cost and process rise as well.
In addition, in the process of applying the encapsulant, the encapsulant will form an upper flow F1 and a lower mold flow F2, respectively, resulting from the separation of the lead frame 11 and the die 12.
Referring to FIG. 1, when the upper and lower mold flows F1 and F2 distribute evenly in the mold cavity formed by the upper mold 14 and lower mold 15, the lead frame 11, die 12 and bonding wires 13 are forced equally, and relative positions thereof with the upper mold 14 and lower mold 15 would not be changed substantially. In this situation, electric elements are successfully enclosed in the mold cavity to achieve the desired package.
However, referring to FIG. 2, in the process of applying the encapsulant, when the lower mold flow F2 is greater than the upper mold flow F1, a lifting force is applied to the flexible lead frame 11, and such a force may change angles of the connecting part 112 between the die pad 111 and leads 113. Extremely, the lifting force may even make the whole die pad 111 convex. The deformation of the lead frame 11 not only changes relative positions between elements but also may make the bonding wires 13 touch the upper mold 14. Thus, such a product becomes defect in view of the exposure of the bonding wires 13 outside the encapsulant 16.
On the other hand, if the upper mold flow F1 is greater than the lower mold flow F2 in the process of applying the encapsulant, as shown in FIG. 3, a pressing force is applied to the flexible lead frame 11, and such a force may also change angles of the connecting part 112 between the die pad 111 and leads 113. Extremely, the pressing force may even make the whole die pad 111 concave. The deformation of the lead frame 11 not only changes relative positions between elements but also may make the die pad 111 touch the lower mold 15. Thus, the exposure of the lead frame 11 outside the encapsulant 16 occurs as well. Furthermore, the bonding wires 13 may be broken because of the deformation of the lead frame 11, and such a product does not fit the requirement of packaging either.
The subject invention is to develop a novel method of manufacturing semiconductor packages to solve the problems of exposures of the bonding wires or lead frame and the semiconductor packages being over thick.
One objective of the present invention is to provide a method of manufacturing semiconductor packages and products thereof. The method of manufacturing comprises steps of: (a) providing a lead frame which comprises a die pad, a plurality of connecting parts and a plurality of leads, wherein the die pad is lower than the leads and connects the leads through the connecting parts, and wherein the die pad comprises at least one supporting structure to fix the lead frame substantially; (b) mounting a die onto the die pad and electrically connecting the lead frame and die by bonding wires; (c) providing an upper mold and a lower mold, wherein the upper mold and lower mold are located at an upper side and a lower side of the leads, respectively, wherein the supporting structures of the die pad are allowed to be supported on the lower mold, and the leads are allowed to protrude outwards from a mold cavity formed by the upper and lower molds; (d) setting the lead frame in steps (a) and (b) onto the lower mold in step (c) and making the supporting structures of the die pad to be supported on the lower mold and then combining the upper mold to the lower mold; (e) applying an encapsulant into the mold cavity formed by the upper and lower molds; and (f) removing the upper and lower molds after encapsulating.
Another objective of the present invention is to provide a lead frame used in a semiconductor package, which comprises a die pad, a plurality of connecting parts and a plurality of leads, wherein the die pad is lower than the leads and connects the leads through the connecting parts, and wherein the die pad comprises at least one supporting structure to fix the lead frame to the lower mold substantially. The present invention can enlarge ranges of the thickness of a die and avoiding the die from being grinded.